The present invention pertains to fuel cells, and more particularly to a direct methanol fuel cell system and a method of fabricating the system, in which electrical energy is produced through the consumption of gaseous or liquid fuels.
Fuel cells in general, are xe2x80x9cbattery replacementsxe2x80x9d, and like batteries, produce electricity through an electrochemical process without combustion. The electrochemical process utilized provides for the combining of hydrogen protons with oxygen from the air. The process is accomplished utilizing a proton exchange membrane (PEM) sandwiched between two electrodes, namely an anode and a cathode. Fuel cells, as known, are a perpetual provider of electricity. Hydrogen is typically used as the fuel for producing the electricity and can be processed from methanol, natural gas, petroleum, or stored as pure hydrogen. Direct methanol fuel cells (DMFCs) utilize methanol, in a gaseous or liquid form as fuel, thus eliminating the need for expensive reforming operations. DMFCs provide for a simpler PEM cell system, lower weight, streamlined production, and thus lower costs.
In a standard DMFC, a dilute aqueous solution of methanol is fed as the fuel on the anode side (first electrode) and the cathode side (second electrode) is exposed to forced or ambient air (or O2). A nafion type proton conducting membrane typically separates the anode and the cathode sides. Several of these fuel cells can be connected in series or parallel depending on the power requirements.
Typically DMFCs designs are large stacks with forced airflow at elevated temperatures. Smaller air breathing DMFC designs are more complicated. In conventional PEM fuel cells, stack connections are made between the fuels cell assemblies with conductive plates, machined with channels or grooves for gas distribution. A typical conventional fuel cell is comprised of an anode (H2 or methanol side) current collector, anode backing, membrane electrode assembly (MEA) (anode/ion conducting membrane/cathode), cathode backing, and cathode current collector. Each fuel cell is capable of approx. 1.0 V. To obtain higher voltages, fuel cells are typically stacked in series (bi-polar manorxe2x80x94positive to negative) one on top another. Conventional fuel cells can also be stacked in parallel (positive to positive) to obtain higher power, but typically, larger fuel cells are simply used.
During operation of a direct methanol fuel cell, a dilute aqueous methanol (usually 3-46 methanol) solution is used as the fuel on the anode side. If the methanol concentration is too high, then there is a methanol crossover problem that will reduce the efficiency of the fuel cell. If the methanol concentration is too low then there will not be enough fuel on the anode side for the fuel cell reaction. Current DMFC designs are for larger stacks with forced airflow. The smaller air breathing DMFC designs are difficult to accomplish because of the complexity in miniaturizing the system for portable applications. For portable applications carrying the fuel in the form of a very dilute methanol mixture would require carrying a large quantity of fuel which is not practical for the design of a miniature power source for portable applications. Miniaturizing the DMFC system requires carrying methanol and water separately and mixing them in-situ for the fuel cell reaction. Recirculation of the water fuel mixture after the fuel cell reaction and recycling of the water generated in the fuel cell reaction, in addition to the water diffused across the membrane is also required for miniaturizing the system.
Accordingly, it is a purpose of the present invention to provide for a direct methanol fuel cell system design in which at least one direct methanol fuel cell is integrated into a miniaturized system.
It is a purpose of the present invention to provide for a direct methanol fuel cell system including microchannels and cavities and microfluidics technology for fuel-bearing fluid mixing, pumping and recirculation.
It is a further purpose of the present invention to provide for a direct methanol fuel cell system which is orientation insensitive.
It is still a further purpose of the present invention to provide for a direct methanol fuel cell system in which all of the system components are embedded inside a base portion, such as a ceramic base portion.
It is yet a further purpose of the present invention to provide for method of fabricating a direct methanol fuel cell system which includes the steps of providing for microchannels and cavities in which microfluidic technology is a basis for the mixing, pumping and recirculation of a fuel-bearing fluid.
The above problems and others are at least partially solved and the above purposes and others are realized in a fuel cell array apparatus and method of forming the fuel cell array apparatus including a base portion, formed of a singular body, and having a major surface. At least one membrane electrode assembly formed on the major surface of the base portion. A fluid supply channel is defined in the base portion and communicating with the at least one membrane electrode assembly for supplying a fuel-bearing fluid to the at least one membrane electrode assembly. An exhaust channel is defined in the base portion and communicating with the at least one membrane electrode assembly. The exhaust channel is spaced apart from the fluid supply channel for exhausting fluid from the at least one membrane electrode assembly. The membrane electrode assembly and the cooperating fluid supply channel and cooperating exhaust channel forming a single fuel cell assembly. There is additionally included a top portion which includes a plurality of electrical components for electrical integration of a plurality of formed fuel cell assemblies.